The objective of Project 4 is to translate the groundbreaking advances in our understanding of epigenetic mechanisms of depression from animal models in the preclinical Projects of this Center to depressed humans, using a postmortem collection of the highest quality and most extensive clinical characterization. Indeed, many of the epigenetic alterations observed to date in the PFC (prefrontal cortex) and NAc (nucleus accumbens) of rodent depression models, derived from Projects 1-3, show similar abnormalities in homologous regions of depressed humans. Conversely, we expect that genome-wide epigenetic analyses of human brain tissue will reveal novel modes of regulation in depressed humans and thereby generate new hypotheses to be tested and characterized functionally in Projects 1-3. The proposed investigations will include genome-wide ChlP-Seq studies of both standard histone modifications and the more advanced chromatin endpoints of interest to our preclinical Projects, as well as RNA-Seq to characterize depression- associated changes in gene expression. Such analyses will be performed on whole extracts of brain regions as well as on isolated neuronal nuclei, using expertise that is uniquely available in our Center. The translation of animal outcomes to human brain disease is even more critical now than ever before, as the field strives to refine the clinical disease itself and to develop novel targets for rational treatments. We will promote the target validation goal of our human studies: 1) by examining how validated chromatin mechanisms cluster with distinct clinical phenotypes of human depression as a way to help generate markers of disease subgroups, and 2) by evaluating the markers more completely throughout the brain circuitry implicated in human depression. In the future, the novel molecular mechanisms of human depression derived from the Center's research on chromatin biology will also help drive efforts in the field to identify biomarkers of depression in living humans. Together, work of Project 4 promises fundamentally new knowledge of the basic molecular and neurobiological mechanisms of depression and of antidepressant treatments that will define new approaches in the field for years to come.